Environmentally insensitive surge suppressor apparatus and method

ABSTRACT

A surge suppressor conducts heat from a surge protection component (SSC) through a heat conductive element, such as a copper pad, on a printed circuit board, to at least one thermal fuse to cause the thermal fuse to open when the resistance of the SSC begins to decrease, resulting in an increase of heat generated by the SSC.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is a Continuation of U.S. patent applicationSer. No. 09/219,213, to Glaser, et al. entitled “ENVIRONMENTALLYINSENSITIVE SURGE SUPPRESSOR APPARATUS AND METHOD” filed Dec. 22, 1998.

TECHNICAL FIELD

[0002] This invention is related to surge suppressors and, moreparticularly, to surge suppressors which provide protection againsttransient voltage and current surges as well as against the failure ofelements of the suppressor itself.

BACKGROUND

[0003] Transient voltages or spikes can be very detrimental toelectronic equipment commonly found in households, businesses, andcommunications networks. Even though each of such spikes may be of avery short duration, a cumulative effect of many such spikes may harmcomponents of the electronic equipment resulting in premature failure ofthe equipment.

[0004] One method of suppressing voltage surges is to use a surgearrestor, or suppression, circuit incorporating solid state surgesuppression elements such as metal oxide varistors, commonly referred toby the acronym MOV. The energy of the surge is then dissipated by theMOV instead of the attached appliances or other circuitry. Such anarrangement works well until the MOV reaches the end of its life. TheMOV averts failure primarily by entering into a low resistance mode.However, in such a mode, the MOV generates a large quantity of heat, andmay ignite a fire or, alternatively, may short line voltage to ground.Such a shorting may cause line protection elements, such as a fuse or acircuit breaker, to blow or trip, respectively, thereby disabling anydownstream circuits or appliances powered by the line voltage. Anydisabling of downstream equipment, especially in commercialapplications, can be disastrous for the user. For example, the disablingof telephone circuitry from operation can result in the loss of millionsof dollars of revenue, and the disabling of life support equipment in ahospital may result in a loss of life. It can be appreciated, therefore,that if an MOV enters into a low resistance mode, it may result incatastrophic consequences. Furthermore, every time that an MOV entersinto a low resistance mode, the probability of catastrophic consequencesoccurring increases. Therefore, it is generally desirable to replace anMOV after it has once entered into a low resistance mode, to therebyavert a possible catastrophic failure. Unfortunately, it is difficult toalways know when an MOV enters into a low resistance mode so that it maybe replaced. While it is difficult to know when an MOV enters into a lowresistance mode, it would be desirable to know when an MOV does fail,and for the effect of such failure on a previously protected circuit tobe minimized.

[0005] Surges in a commercial environment are typically suppressed onthe AC voltage lines of primary and secondary AC distribution panels toprotect sensitive equipment which receive power from the suchdistribution power panels. Such surge suppression is essentially mountedin parallel to electronic equipment and provides an easy or quick pathfor lightning and transient surges to divert to ground instead ofdamaging sensitive electronic equipment that often comprise electricallysensitive semiconductor chips. Surge suppression circuitry mounted insuch a manner generally comprises four basic states of operation:

[0006] 1. Normal State—There is a high impedance path between ground andAC power. Current leakage is in the range of microamps. Heat is not anissue. The voltage level applied to the suppression circuitry is below aturn-on voltage of the surge suppressor.

[0007] 2. High Voltage Transient Turn On State—A very low impedance pathbetween a voltage source and ground occurs for micro-seconds, providinga low impedance path for transient energy. Transient surge voltage mustexceed the turn on level of the suppression circuitry for this state tooccur. Heat is a byproduct of diverting a large amount of transientenergy to ground even though the impedance level is low. When the surgeis of a short duration, the heat is not normally destructive in nature.The total power consumed in generating heat is less than the amountrequired to trip or blow breaker/fuse protective circuits.

[0008] 3. Permanent Failure—A very low impedance path between a voltagesource and ground. The low impedance path of the surge suppressor allowsa sufficiently high level of energy to blow or trip a fuse/breakerprotective circuit. If protection against excessive current is not apart of the surge suppressor design, then fuses or circuit breakersfound in the AC distribution panel will be blown off-line, hopefullypreventing hazardous conditions such as an electrical fire fromdeveloping. Unfortunately this also turns off important electroniccircuitry downstream.

[0009] 4. Catastrophic Failure—A dangerous amount of heat is developedfrom the surge suppression device from a limited current passing throughthe surge suppressor to ground. This current may be limited because ofoutside voltage conditions (i.e., tree fallen on a power pole) where theexcessive voltage is sufficient to turn on the surge suppressor for morethan a few micro-seconds but still having only a limited amount ofcurrent well-below the fuse, or in-line breaker, ratings. This is anoverheat condition which can also occur in a surge suppressor componentthat is near its end of life and that has failed toward a shortedcondition (“low” but not “very low” impedance) but has not failedtotally shorted. The “low” impedance to a normally applied voltageallows a limited current to flow through the surge suppression deviceand allows a huge amount of heat to develop within the surge suppressorcomponent thereby causing dangerous conditions such as smoke and fire toexist.

[0010] The use of internal thermal fuses (also known as thermalswitches) in the surge suppression circuitry eliminates the weakness inboth steps 3 and 4 above. A thermal fuse not only acts like a normalfuse which will blow in a permanent failed condition with normal inrushcurrent conditions, but will also sense the build-up of heat leading toa catastrophic failure of a surge suppressor component.

[0011] The encapsulation of surge suppression circuitry in epoxy, andthe placement of surge suppression circuitry in a silica sandenvironment, rather than in an air environment, is now an industrystandard among most companies that produce surge suppression devices.The primary reason is that the sudden superheating of air adjacent anoverheated surge suppressor inside a sealed environment has resulted inexplosions of the container incorporating the surge suppressioncircuitry and has ignited fires both inside and outside the container.The technique of fully encapsulating surge suppression circuitry inepoxy, however, doesn't allow any thermal expansion of the circuitcomponents and, in catastrophic failure conditions, causes dangerousexplosive conditions to exist. Silica sand is a poor conductor of heat(an insulator) but acts as a good smothering agent in case of fireinside of the surge suppression circuitry container.

[0012] Various attempts have been made in the prior art to use a thermalfuse to sense when an MOV is approaching the end of its life so thatpower may be removed from the MOV prior to any failure of the MOV.Typically, this is achieved by detecting heat radiated from the MOV,which heat is indicative of the MOV entering a low resistance mode. Suchan approach has been found to be very unreliable for circuitry which maybe subjected to a wide range of environmental mediums and temperatures.Further, humidity and barometric pressure, when the environment is air,can affect the temperature at which a radiated heat sensitive thermalfuse operates. Finally, the spacing between the thermal fuse and the MOVis critical. Mislocations or accidental dislocations of this spacing maycause the MOV to become so hot that it will burst into flames before thethermal fuse is activated to an open condition. As known to many in theart, the thermal fuse commonly used not only opens at a given settemperature such as 200 degrees F., it may have a current rating of somevalue such as 15 amperes. The current rating used in the industry is afunction of time as well as current (i.e., it is really a powersensitive fuse). Thus such a device may not open even though a currentsurge in the range of thousands of amperes flows through the device ifthe time is very short such as a few microseconds.

[0013] As used in this application, the term “environment” will be usedto refer to all factors that may affect the radiation or transfer ofheat away from the surface of a surge suppression component. As is knownto those skilled in the art, surge suppression circuitry may be open tothe air or enclosed in a sealed container. Further the surge suppressioncircuitry components may be encased in a potting compound or otherwisesurrounded by a dielectric other than air such as silica sand. Each ofthese conditions substantially affects the rate of radiant heat transferfrom a heat source to an adjacent radiant heat sensor.

[0014] Also used in this application, the term surge suppressioncomponent (“SSC”) will be used to refer to any device that performs thefunction of surge suppression (also known as surge protection) includingmetal oxide varistors (MOV's), carbon based suppressors, avalanche baseddiodes, Transorbs™, gas tubes, and the like.

[0015] One of the more difficult problems in physically locating athermal fuse relative to heat-dissipating SSC's, such as an MOV, occurswhen silica sand is used as a dielectric insulator inside the product.As mentioned above, silica has become an industry standard method usedto minimize the risk of heat rising too fast within the closed confinesof a sealed box wherein the pressures generated by the heat could causean explosion. When silica sand is used as part of a safety technique,the heat transferring capability of the component to the environmentaround the component is completely changed from what it would be withoutthe silica sand. Thus, prior art surge suppressors were required to usedifferent designs and component placements in accordance with thespecific environment the circuit would be subjected to in end use. Sucha multiplicity of designs resulted in great inefficiencies in productionthereby increasing end product costs. Furthermore, since silica sand isan insulator, the spacing is more critical than it is in air for radiantheat sensing of an overheat condition of the SSC.

[0016] Some prior art circuits have attempted to utilize the increasedcurrent-carrying capacity of two thermal fuses connected in parallel ina manner similar to that shown in FIG. 1. Such a circuit has beenimplemented by placing the two thermal fuses on opposite sides of theheat producing element (i.e., the MOV). However, this approach createdmany problems in accurately locating the thermal fuses with respect tothe MOV such that they would both open at substantially the same time.The result was that an explosion often occurred before radiant heatopened the second thermal fuse. The location problem was exacerbated bythe use of silica sand as an insulating dielectric between the MOV andthe adjacent thermal fuses.

[0017] It has also been found that, when a single thermal fuse is usedin series with an MOV, a voltage surge may destroy (i.e., open) thethermal fuse even though the MOV is still operational.

[0018] It would thus be desirable to provide a more reliable method oftransferring heat from a surge suppression component (SSC) to a thermalfuse whereby the surface temperature of the SSC varies over a smallerrange under environmental temperature extremes before an associatedthermal fuse opens. It would be further desirable to have a circuit thatoperates in a consistent or predictable manner over a wide range ofenvironments (such as both air and silica sand). It would also bedesirable to provide a surge suppression circuit design that allows thefailure of a thermal fuse component while still providing surgesuppression for the connected line and associated downstream circuits orequipment.

SUMMARY OF THE INVENTION

[0019] The present invention minimizes the effects of environmentalfactors which influence the opening of a thermal fuse in a surgesuppressor prior to failure of a surge suppression component (SSC) ofthe surge suppressor. According to the present invention, this is doneby conducting heat between leads of the thermal fuse and the SSC, ratherthan radiating heat through the environment, to cause the thermal fuseto open. Such an approach allows greater freedom in component placementon a printed circuit board and minimizes delays in the opening of thethermal fuse due to the location of the thermal fuse relative to the SSCor due to the use of an environment other than an environment for whichthat surge suppressor was specifically designed.

[0020] In an alternate embodiment of the invention, an array of thermalfuses are connected in parallel so that, if one thermal fuse fails, thecircuit will still remain functional. Since a majority of the current ina transient surge typically travels through one SSC having the lowestresistance of an array of SSC's connected in parallel, the array ofthermal fuses connected in parallel permit one thermal fuse to openwithout causing the remaining thermal fuses to open.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] For a more complete understanding of the present invention, andthe advantages thereof, reference is now made to the followingdescriptions taken in conjunction with the accompanying drawings, inwhich:

[0022]FIG. 1 is an elevational view of a surge suppressor embodyingfeatures of the prior art;

[0023]FIG. 2 is a perspective view of surge suppressor embodyingfeatures of the present invention;

[0024]FIG. 3 is a schematic diagram of an alternate embodiment of thepresent invention in which two thermal fuses are utilized;

[0025]FIG. 4 is a plan view of a printed circuit board exemplifying howthe embodiment of FIG. 3 may be physically laid out;

[0026]FIG. 5 is a schematic diagram of an alternate embodiment of thepresent invention in which four thermal fuses are utilized inconjunction with an indicator which indicates the operational status ofthe surge suppressor;

[0027]FIG. 6 is a schematic diagram of an alternate embodiment of thepresent invention in which two thermal fuses are utilized in conjunctionwith an indicator that indicates the operational status of the surgesuppressor and a gas tube that is connected between a neutral and aground terminal;

[0028]FIG. 7 is a schematic diagram of an alternate embodiment of thepresent invention in which two thermal fuses are utilized in conjunctionwith a gas tube connected in series with an inductor; and

[0029]FIG. 8 is a schematic diagram of an alternate embodiment of thepresent invention in which four thermal fuses are utilized as twothermal fuse pairs in parallel in conjunction with a gas tube connectedin series with a resistor.

DETAILED DESCRIPTION

[0030] Referring to FIG. 1 of the drawings, the reference numeral 10generally designates a surge suppressor embodying features of the priorart. The surge suppressor 10 includes a printed circuit board (PCB) 11on which are mounted a first surge suppression component (SSC) 12, suchas a varistor, a second SSC 14, such as a varistor, and a thermal fuse16 (also known as a thermal switch). While not shown, additional SSC'smay connected in parallel with the SSC's 12 and 14 to increase thesurge-handling capacity of the surge suppressor 10. The SSC 12 includestwo leads 18 and 20, and the SSC 14 includes two leads 24 and 26, allfour of which leads are soldered to the PCB 11. The thermal fuse 16includes a first lead 22 and a second lead 28 which are also soldered tothe PCB 11 (though the soldering of only the first lead 22 is shown inFIG. 1). In practice, the lead 22 is electrically connected via the PCB11 to the leads 20 and 26 of the SSC's 12 and 14, respectively.Dielectric mediums 13 and 15, such as air, silica sand, or the like,having a thickness of L1 and L2, respectively, are interposed betweenthe thermal fuse 16 and the SSC's 12 and 14, respectively.

[0031] In operation, when sufficient current passes through the SSC's 12and 14 to heat the SSC's, heat is transferred through the dielectricmediums 13 and 15 to the thermal fuse 16, thereby causing thetemperature of the thermal fuse to rise. When the temperature of thethermal fuse 16 reaches a predetermined level, the thermal fuse opens,and cuts off the flow of current through the SSC's 12 and 14.

[0032] A drawback with the foregoing surge suppressor 10 is that, tomaintain consistent operation, the thickness L1 and L2 of the dielectricmediums 13 and 15, respectively, must be maintained within limits whichare determined based on the choice of the dielectric mediums 13 and 15,and of the SSC's 12 and 14, used. A minor variation of the thicknessesL1 and L2 will cause the thermal fuse 16 to open too soon, rendering theSSC's less useful, or to open too late, thereby either shorting theSSC's or igniting the SSC's on fire. For example, if the thicknesses L1or L2 are too large or if an incorrect dielectric 13 or 15 is used, thethermal fuse 16 may not open until after one or both of the SSC's 12 and14 have shorted and/or caught fire. Another drawback is that if, in theenvironment of the surge suppressor 10, the temperature is very lowand/or the humidity is very high, then the heat radiated from the SSC's12 and 14 will not raise the temperature of the thermal fuse 16 asquickly as it might otherwise, and the SSC's may experience catastrophicfailure. Yet another drawback of the surge suppressor 10 shown in FIG. 1is that, due to the requirement that the thermal fuse be physicallylocated very close to the SSC's 12 and 14, the surge suppressor 10 cannot be readily adapted to handle additional SSC's or thermal fuses byparallel connections.

[0033] In FIG. 2, a surge suppressor of the present invention is shownwhich provides for a more robust and reliable medium through which heatmay be transferred from an SSC to a thermal fuse. Accordingly, the surgesuppressor shown in FIG. 2, designated by the reference numeral 30,includes a printed circuit board (PCB) 32 on which is mounted anelectrical component such as a suitable SSC 34, such as a metal oxidevaristor (MOV), carbon based suppressor, avalanche based diode,Transorb™, gas tube, or the like, well-known in the art, having a firstlead line 34 a and a second lead line 34 b. The first lead line 34 a iselectrically connected via a first trace 35 to a first terminal 42configured for connection to a neutral or ground line (not shown),depending upon the circuit application. The second lead line 34 b iselectrically and thermally connected via a circuit conductor, or pad, 36to a first lead line 38 a of a thermal fuse 38. The pad 36 may compriseany material which is suitable for conducting both electricity and heat.The pad 36 may thus be fabricated as any trace on the PCB 32 would befabricated in a conventional manner using substantially the samematerial, such as copper or other suitable metal effective forconducting both heat and current. The thermal fuse 38 includes a secondlead line 38 b which electrically connects the thermal fuse 38 via asecond trace 40 to a second terminal 44 configured for connection toline voltage (not shown).

[0034] It is to be understood that, while the terminal 42 is describedherein as connected to ground or neutral, and the terminal 44 asconnected to line voltage, the terminal 42 may be connected to linevoltage, and the terminal 44 connected to neutral or ground. It is to bestill further understood that voltage applied to the circuit 30 may beeither AC or DC. SSC's, thermal conductors, and thermal fuses, takenindividually, and the operation of such, operating individually, areconsidered to be well-known in the art and, therefore, will not bediscussed in greater detail.

[0035] As discussed further below, if it would be desirable to increasethe current-carrying capacity of the surge suppressor 30, additionalSSC's (not shown in FIG. 2) may be connected in parallel across the SSC34, and additional thermal fuses (not shown in FIG. 2) may be connectedin parallel across the thermal fuse 38.

[0036] In operation, the terminal 44 is connected to line voltage (notshown) and the terminal 42 is connected to a neutral or ground line (notshown), depending upon the circuit application. As a voltage potentialis applied across the terminals 42 and 44, and current begins to flowthrough the surge suppressor 30, the temperature of the SSC 34 rises. Asthe temperature of the SSC 34 rises, heat is generated which istransferred from the SSC 34 through the pad 36 to the thermal fuse 38.Under normal operating conditions, the temperature of the SSC 34 and,thus, also of the thermal fuse 38, stabilizes and does not continue torise beyond an acceptable temperature, thereby permitting current tocontinue to flow through the surge suppressor 30 for an indefiniteperiod of time.

[0037] If the line voltage across the terminals 42 and 44 exceeds thevoltage for which the surge suppressor was designed for under normaloperating conditions, then the temperature of the SSC 34 rises beyond anacceptable level, and greater heat is generated and transferred from theSSC 34 via the pad 36 to the thermal fuse 38, thereby causing thethermal fuse to rise in temperature beyond an acceptable level. When thetemperature of the thermal fuse 38 rises to such a level, it preventsfurther current from flowing through the surge suppressor, therebyprotecting the SSC's from excessive current flow which could destroy theSSC and potentially ignite a fire.

[0038] By the use of the surge suppressor 30 shown in FIG. 2, whereinheat is conducted through the pad 36 rather than radiated through air aspracticed in the prior art, the thermal fuse 38 may be physicallypositioned anywhere on the PCB 32 without regard to the position of theSSC 34. Therefore, the surge suppressor 30 can be manufactured andmaintained more economically than is possible under the prior art, suchas illustrated in FIG. 1. Furthermore, because the performance of thesurge suppressor 30 is not sensitive to the position of the thermal fusewith respect to the SSC 34, the surge suppressor 30 is more reliable andits performance is more predictable than that of the prior art. Still,further, the surge suppressor 30 permits additional SSC's and/or thermalfuses to be more readily added to the surge suppressor 30, as discussedbelow, than is possible under the prior art.

[0039] Alternate embodiments of the surge suppressor 30 of the presentinvention are shown in FIGS. 3-9, in which identical components aregiven the same reference numerals. According to the embodiment of FIG.3, the surge suppressor 30 is adapted for handling a greater flow ofcurrent than the embodiment shown in FIG. 2. To this end, an additionalthermal fuse 46 is connected in parallel with the thermal fuse 38.Otherwise, the embodiment of FIG. 3 is identical to that of FIG. 2.Operation of the surge suppressor 30 shown in FIG. 3 is similar to theoperation of the surge suppressor shown in FIG. 2, the only materialdifference being that the surge suppressor shown in FIG. 3 can handle agreater flow of current.

[0040]FIG. 4 exemplifies how the embodiment shown in FIG. 3 may bephysically laid out on the PCB 32 and, more particularly, how far theSSC 34 may be physically removed from the thermal fuses 38 and 46.Accordingly, the PCB 32 includes the terminals 42 and 44, and arelatively wide heat-transferring pad 36. The thermal fuses 38 and 46are connected in parallel between the terminal 44 and the pad 36, andthe SSC 34 is connected between pad 36 and the terminal 42. A dashedline 32 a represents other components of the PCB 32. It can beappreciated from an examination of FIG. 4 that, unlike the prior artsurge suppressor 10 depicted in FIG. 1, the SSC 34 may be relatively farremoved from the thermal fuses 38 and 46. As a result of the distanceseparating the SSC 34 and the thermal fuses 38 and 46, a longer periodof time is required for heat to be transferred from the SSC 34 to thethermal fuses 38 and 46. As the temperature of the SSC 34 rises prior tofailure, there will be a lag time for the heat to transfer to thethermal fuses 38 and 46. Such a lag may be accounted for by designingthe thermal fuses 38 and 46 to blow at a suitable temperature below thetemperature at which the SSC 34 would fail.

[0041] In addition to the advantages described above with respect to theprevious embodiment shown in FIG. 2, the embodiments shown in FIGS. 3-4illustrate how the current-carrying capacity of the present inventionmay be readily increased as desired. Moreover, if one thermal fuse 38 or46 fails, the surge suppressor 30 will still remain viable.

[0042] According to the embodiment of FIG. 5, the surge suppressor 30 isadapted for handling a greater flow of current than the embodiment shownin any of FIGS. 2-4, and is provided with an indicator effective forindicating when then surge suppressor is operative. To that end, threeadditional thermal fuses 46, 48, and 50 are connected in parallel acrossthe thermal fuse 38, and an additional SSC 52 is connected between thepad 36 and a ground 54. An indicator 56, such as a neon light, isconnected in parallel across the SSC 34. While not shown and generallynot necessary, an additional indicator may also be connected in parallelacross the SSC 52. Line voltage is connected to the terminal 44 andneutral is connected to the terminal 42, as in FIG. 2. Operation of thesurge suppressor 30 shown in FIG. 5 is similar to the operation of thesurge suppressor shown in FIG. 2, the only material difference beingthat the surge suppressor shown in FIG. 5 can handle a greater flow ofcurrent, and activation or illumination of the indicator 56 indicatesthat the surge suppressor 30 is operational.

[0043] According to the embodiment of FIG. 6, the additional thermalfuse 46 is connected in parallel across the thermal fuse 38, and theindicator 56 is connected in parallel across the SSC 34. Additionally, agas tube 58 having a breakdown voltage well-known in the art, isconnected between the neutral 42 and the ground terminal 54. Inoperation, if the surge suppressor 30 receives a voltage spikesufficient to cause the potential between the neutral terminal 42 andthe ground terminal 54 to exceed the breakdown voltage of the gas tube58, then the gas tube “breaks down” and shunts energy from the spike tothe ground terminal 54.

[0044] According to the embodiment of FIG. 7, the additional thermalfuse 46 is connected in parallel across the thermal fuse 38, and the gastube 58 is connected in series with an inductor 60 between the terminals42 and 44 to provide additional high-voltage AC protection, even whenthe SSC 34 fails (i.e., overheats) and causes the thermal fuses 38 and46 to blow open. An additional SSC 62 is connected between the neutralterminal 42 and the ground terminal 54. In operation, when there is atransient surge, the SSC 34 initially absorbs the surge for a fewmicroseconds. If the transient lasts for more than a few microseconds,then the gas tube 58 enters an arc mode and absorbs the additionalcurrent. The SSC 62 will activate any time there is a transient surgeinduced on the neutral terminal 54 referenced to ground. When thetransient surge subsides, AC is impeded by the inductor 58, and the gastube 58 exits the arc mode.

[0045] According to the embodiment of FIG. 8, the additional thermalfuse 46 is connected in parallel across the thermal fuse 38, and the gastube 58 is connected in series with a resistor 62 between the terminals42 and 44. Two additional thermal fuses 138 and 146 are connected inparallel between the pad 36 and an additional conductive pad 136. Anadditional SSC 134 is connected between the pad 136 and the ground 54.In operation, the thermal fuses 38 and 46 protect the SSC 34 againstline-to-neutral surges, and the thermal fuses 138 and 146 protect theSSC 134 against neutral-to-ground surges. Thus, all-mode protection isobtained because all phases are protected. Depending on the distance ofthe thermal fuses 138 and 146 from the SSC 34, the thermal fuses 138 and146 may also protect the SSC 34 against line-to-neutral surges.

[0046] Having thus described the present invention by reference tocertain of its preferred embodiments, it is noted that the embodimentsdisclosed are illustrative rather than limiting in nature and that awide range of variations, modifications, changes, and substitutions arecontemplated in the foregoing disclosure and, in some instances, somefeatures of the present invention may be employed without acorresponding use of the other features. Many such variations andmodifications may be considered obvious and desirable by those skilledin the art based upon a review of the foregoing description of preferredembodiments. Accordingly, it is appropriate that the appended claims beconstrued broadly and in a manner consistent with the spirit and scopeof the invention.

1. A surge suppressor comprising: a thermally and electricallyconductive pad bonded to a printed circuit board (PCB); an electricalcomponent thermally connected to the conductive pad; and at least onethermal fuse thermally and electrically connected to the conductive padto receive from the electrical component, via the conductive pad, heatto increase the temperature of the at least one thermal fuse, thethermal fuse being configured to open in response to heat transferredthrough the pad.
 2. The surge suppressor of claim 1 wherein the at leastone thermal fuse is connected in series with the electrical component.3. The surge suppressor of claim 1 wherein the electrical component isthermally connected to the conductive pad via a lead line connected tothe electrical component, and the thermal fuse is thermally connected tothe conductive pad via a lead line connected to the thermal fuse.
 4. Thesurge suppressor of claim 1 wherein the electrical component is a surgesuppression component.
 5. The surge suppressor of claim 1 wherein theelectrical component is a surge suppression component selected from thegroup consisting of a metal oxide varistor (MOV), a diode, and a gastube.
 6. The surge suppressor of claim 1 wherein the at least onethermal fuse comprises at least two thermal fuses connected in parallel.7. The surge suppressor of claim 1 wherein the predetermined temperatureof the thermal fuse is correlated with a predetermined temperature ofthe electrical component which would precipitate failure of theelectrical component.
 8. The surge suppressor of claim 1 furthercomprising an indicator connected in parallel across the electricalcomponent to indicate operation of the surge suppressor.
 9. The surgesuppressor of claim 1 further comprising an neon light connected inparallel across the electrical component to indicate operation of thesurge suppressor.
 10. The surge suppressor of claim 1 further comprisingan neon light connected in parallel across the electrical component toindicate operation of the surge suppressor, and an additional electricalcomponent connected between the conductive pad and a ground terminal.11. The surge suppressor of claim 1 further comprising a gas tubeconnected in series between the electrical component and a groundterminal.
 12. The surge suppressor of claim 1 further comprising aserially connected gas tube and inductor connected in parallel acrossthe electrical component and the at least one thermal fuse; and whereinthe electrical component is a first electrical component and a secondelectrical component is connected in series between the first electricalcomponent and a ground terminal.
 13. The surge suppressor of claim 1further comprising a serially connected gas tube and resistor connectedin parallel across the electrical component and the at least one thermalfuse; and wherein the electrical component is a first electricalcomponent, the conductive pad is a first conductive pad, and a secondelectrical component is connected in series via a second conductive padwith an additional at least one thermal fuse between the firstconductive pad and a ground terminal.
 14. The surge suppressor of claim1 wherein the conductive pad comprises copper.
 15. The method of claim 1wherein the thermal fuse opens prior to combustion of the electricalcomponent.
 16. The method of claim 1 wherein the heat is generated by ahigh electrical voltage and limited current flowing through theelectrical component.
 17. The method of claim 1 wherein the heat isgenerated internally by current flowing through the thermal fuse. 18.The method of claim 15 wherein the heat is generated by at least one orboth of a high electrical voltage and limited current flowing throughthe electrical component and current flowing through the thermal fuse.19. The surge suppressor of claim 1 wherein the thermal fuse isconfigured to open in response to heat transferred through theconductive pad rather than heat radiated through the environment.
 20. Amethod for preventing an electrical component mounted on a printedcircuit board from destructively overheating, comprising the steps of:attaching a lead line of the electrical component to a thermally andelectrically conductive pad mounted on a printed circuit board;attaching a lead line of at least one thermal fuse to the conductive padto permit heat generated by the electrical component to transfer throughthe conductive pad to the at least one thermal fuse; and configuring theat least one thermal fuse to open in response to heat received from theelectrical component through the pad.
 21. The method of claim 20 whereinthe step of attaching a lead line of at least one thermal fuse to theconductive pad further comprises attaching a lead line of at least twothermal fuses connected in parallel to the conductive pad.
 22. Themethod of claim 20 wherein the electrical component is an element of asurge suppressor.
 23. The method of claim 20 wherein the electricalcomponent is a surge suppression component.
 24. The method of claim 20wherein the electrical component is selected from the group consistingof a metal oxide varistor (MOV), a diode, and a gas tube.
 25. The methodof claim 20 wherein the conductive pad comprises copper.
 26. The methodof claim 20 further comprising the step of positioning the at least onethermal fuse relative to the electrical component so that the quantityof heat conducted from the electrical component to the at least onethermal fuse exceeds the quantity of heat radiated from the electricalcomponent to the at least one thermal fuse.
 27. The method of claim 20further comprising the step of correlating the predetermined temperatureof the thermal fuse with a predetermined temperature of the electricalcomponent which would precipitate failure of the electrical component.28. The method of claim 20 further comprising connecting an indicator inparallel across the electrical component to indicate operation of thesurge suppressor.
 29. The method of claim 20 further comprisingconnecting a neon light in parallel across the electrical component toindicate operation of the surge suppressor.
 30. The method of claim 20further comprising connecting a neon light in parallel across theelectrical component to indicate operation of the surge suppressor, andconnecting an additional electrical component between the conductive padand a ground terminal.
 31. The method of claim 20 further comprisingconnecting a gas tube in series between the electrical component and aground terminal.
 32. The method of claim 20 further comprisingconnecting a serially connected gas tube and inductor in parallel acrossthe electrical component and the at least one thermal fuse; and whereinthe electrical component is a first electrical component and the methodfurther comprises connecting a second electrical component in seriesbetween the first electrical component and a ground terminal.
 33. Themethod of claim 20 further comprising connecting a serially connectedgas tube and resistor in parallel across the electrical component andthe at least one thermal fuse; and wherein the electrical component is afirst electrical component, the conductive pad is a first conductivepad, and the method further comprises connecting a second electricalcomponent in series via a second conductive pad with an additional atleast one thermal fuse between the first conductive pad and a groundterminal.
 34. The method of claim 20 wherein the thermal fuse opensprior to combustion of the electrical component.
 35. The method of claim20 wherein the heat is generated by a high electrical voltage andlimited current flowing through the electrical component.
 36. The methodof claim 20 wherein the heat is generated internally by current flowingthrough the thermal fuse.
 37. The method of claim 34 wherein the heat isgenerated by at least one or both of a high electrical voltage andlimited current flowing through the electrical component and currentflowing through the thermal fuse.
 38. The method of claim 20 wherein thethermal fuse opens in response to heat received through the conductivepad rather than heat radiated through the environment.
 39. A method forprotecting a circuit by preventing an electrical component mounted on aprinted circuit board (PCB) from overheating, comprising the steps of:attaching one lead line of the electrical component to a thermally andelectrically conductive pad bonded to the PCB; and permitting heat to beconducted from the conductive pad to a lead line of at least one thermalfuse configured to open in response to heat received through the padfrom the electrical component.
 40. The method of claim 39 wherein the atleast one thermal fuse further comprises at least two thermal fusesconnected in parallel.
 41. The method of claim 39 wherein the electricalcomponent is an element of a surge suppressor.
 42. The method of claim39 wherein the electrical component is a surge suppression component.43. The method of claim 39 wherein the electrical component is selectedfrom the group consisting of a metal oxide varistor (MOV), a diode, anda gas tube.
 44. The method of claim 39 wherein the conductive padcomprises copper.
 45. The method of claim 39 further comprising the stepof positioning the at least one thermal fuse relative to the electricalcomponent so that the quantity of heat conducted from the electricalcomponent to the at least one thermal fuse exceeds the quantity of heatradiated from the electrical component to the at least one thermal fuse.46. The method of claim 39 further comprising the step of correlatingthe predetermined temperature of the thermal fuse with a predeterminedtemperature of the electrical component which would precipitate failureof the electrical component.
 47. The method of claim 39 furthercomprising connecting an indicator in parallel across the electricalcomponent to indicate operation of the surge suppressor.
 48. The methodof claim 39 further comprising connecting a neon light in parallelacross the electrical component to indicate operation of the surgesuppressor.
 49. The method of claim 39 further comprising connecting aneon light in parallel across the electrical component to indicateoperation of the surge suppressor, and connecting an additionalelectrical component between the conductive pad and a ground terminal.50. The method of claim 39 further comprising connecting a gas tube inseries between the electrical component and a ground terminal.
 51. Themethod of claim 39 further comprising connecting a serially connectedgas tube and inductor in parallel across the electrical component andthe at least one thermal fuse; and wherein the electrical component is afirst electrical component and the method further comprises connecting asecond electrical component in series between the first electricalcomponent and a ground terminal.
 52. The method of claim 39 furthercomprising connecting a serially connected gas tube and resistor inparallel across the electrical component and the at least one thermalfuse; and wherein the electrical component is a first electricalcomponent, the conductive pad is a first conductive pad, and the methodfurther comprises connecting a second electrical component in series viaa second conductive pad with an additional at least one thermal fusebetween the first conductive pad and a ground terminal.
 53. The methodof claim 39 wherein the thermal fuse opens prior to combustion of theelectrical component.
 54. The method of claim 39 wherein the heat isgenerated by a high electrical voltage and limited current flowingthrough the electrical component.
 55. The method of claim 39 wherein theheat is generated internally by current flowing through the thermalfuse.
 56. The method of claim 53 wherein the heat is generated by atleast one or both of a high electrical voltage and limited currentflowing through the electrical component and current flowing through thethermal fuse.
 57. The method of claim 39 wherein the thermal fuse isconfigured to open in response to heat received through the conductivepad rather than heat radiated through the environment.
 58. A surgesuppressor comprising: a thermally and electrically conductive padbonded to a printed circuit board (PCB); an electrical componentthermally and electrically connected to the conductive pad; and at leastone thermal fuse thermally and electrically connected to the conductivepad to receive heat from the electrical component via the conductivepad, the thermal fuse being configured to open in response to heattransferred through the pad from an external source.
 59. The surgesuppressor of claim 58 wherein the at least one thermal fuse isconnected in series with the electrical component.
 60. The surgesuppressor of claim 58 wherein the electrical component is thermallyconnected to the conductive pad via a lead line connected to theelectrical component, and the thermal fuse is thermally connected to theconductive pad via a lead line connected to the thermal fuse.
 61. Thesurge suppressor of claim 58 wherein the electrical component is a surgesuppression component.
 62. The surge suppressor of claim 58 wherein theelectrical component is a surge suppression component selected from thegroup consisting of a metal oxide varistor (MOV), a diode, and a gastube.
 63. The surge suppressor of claim 58 wherein the at least onethermal fuse comprises at least two thermal fuses connected in parallel.64. The surge suppressor of claim 58 wherein the predeterminedtemperature of the thermal fuse is correlated with a predeterminedtemperature of the electrical component which would precipitate failureof the electrical component.
 65. The surge suppressor of claim 58further comprising an indicator connected in parallel across theelectrical component to indicate operation of the surge suppressor. 66.The surge suppressor of claim 58 further comprising an neon lightconnected in parallel across the electrical component to indicateoperation of the surge suppressor.
 67. The surge suppressor of claim 58further comprising an neon light connected in parallel across theelectrical component to indicate operation of the surge suppressor, andan additional electrical component connected between the conductive padand a ground terminal.
 68. The surge suppressor of claim 58 furthercomprising a gas tube connected in series between the electricalcomponent and a ground terminal.
 69. The surge suppressor of claim 58further comprising a serially connected gas tube and inductor connectedin parallel across the electrical component and the at least one thermalfuse; and wherein the electrical component is a first electricalcomponent and a second electrical component is connected in seriesbetween the first electrical component and a ground terminal.
 70. Thesurge suppressor of claim 58 further comprising a serially connected gastube and resistor connected in parallel across the electrical componentand the at least one thermal fuse; and wherein the electrical componentis a first electrical component, the conductive pad is a firstconductive pad, and a second electrical component is connected in seriesvia a second conductive pad with an additional at least one thermal fusebetween the first conductive pad and a ground terminal.
 71. The surgesuppressor of claim 58 wherein the conductive pad comprises copper. 72.The method of claim 58 wherein the thermal fuse opens prior tocombustion of the electrical component.
 73. The method of claim 58wherein the heat is generated by a high electrical voltage and limitedcurrent flowing through the electrical component.
 74. The method ofclaim 58 wherein the heat is generated internally by current flowingthrough the thermal fuse.
 75. The method of claim 72 wherein the heat isgenerated by at least one or both of a high electrical voltage andlimited current flowing through the electrical component and currentflowing through the thermal fuse.
 76. A method for preventing anelectrical component mounted on a printed circuit board fromdestructively overheating, comprising the steps of: attaching a leadline of the electrical component to a thermally and electricallyconductive pad mounted on a printed circuit board; attaching a lead lineof at least one thermal fuse to the conductive pad to permit heatgenerated by the electrical component to transfer through the conductivepad to the at least one thermal fuse; and configuring the at least onethermal fuse to open when the temperature of the at least one thermalfuse exceeds a predetermined temperature in response to heat receivedfrom the electrical component through the pad.